Vacuum tube



ly 2, 1940- A. SENAUKE 2,206,649

' VACUUM TUBE Filed Oct. 14, 1936 F l G. 2 44 44 45 INVENTOR r/LEXAND 'l? J: HUKE FI'GJ. yfl /g ATTORNEY.

Patented July 2, 1940 UNITED STATES PATENT OFFICE VACUUM TUBE Alexander Senauke, New York, N. Y., assignor to Ampere X Electronic Products, Inc., Brooklyn, N. Y., a corporation of New York Application October 14, 1936, Serial No. 105,475

4 Claims. (Cl. 25027.5)

This invention relates to vacuum tubes, and frequencies and under conditions where tubes more especially to vacuum tubes capable of opof the usual construction quickly develop strucerating at ultra-high frequencies, and of delivtural failure. ering relatively large amounts of power at such Still other objects and advantages of my infrequencies, without requiring expensive and vention will be apparent from the following 5 cumbersome arrangements for water-cooling the specification. tubes. The features of novelty which I believe to be When tubes are desired to operate at ultracharacteristic of my invention are particularly high frequencies, such as above 20 megacycles, pointed out in the appended claims, My invenmany obstacles are encountered to satisfactory tion itself, however, both as to its fundamental 10 operation, among the most important of which principles and as to its particular embodiments, is the heating effect from dielectric losses, which is described in the specification and accompanybecomes extremely important, and may in pracing drawing, in which:

tice, determine the safe rating of the tube. Fig. 1 is a front elevation, partly broken away,

1| By designing the tube so as to reduce the variof a tube in accordance with my invention; ous internal capacities of the tube it is possible Fig. 2 is a detail side elevation of the anode to provide tubes which will operate at very high end of the tube of Fig. 1, partly broken away; frequencies, but such tubes are characterized by Fig. 3 is a section on lines 3-3 of Fig. 1, and very small electrodes, and are incapable of de- Fig. 4 is a detail horizontal cross section on go livering any substantial power. enlarged scale of the clamping collar.

In accordance with my invention, I provide In the design of vacuum tubes, two factors are vacuum tubes which are so constructed that the of importance; first, the frequency at which the internal electrodes may be made relatively large tube will deliver power, and second, the quantity with consequent high heat dissipating capacity, of power which the tube will deliver in susand at the same time, the tube is capable of optained operation without a rise in temperature erating at ultra-high frequencies, contrary to. sufficient to cause failure or material shortening present beliefs. By virtue of certain changes of useful life. from the usual practice in design and produc- These two factors are not independent. On tion of the tubes, I have succeeded in eliminating the contrary, they are closely inter-related. For many of the causes of excessive heating and reexample, an attempt to use a tube in sustained 3Q sultant failure of tubes in such use, so that it operation at frequencies at which it will funcis possible to satisfactorily utilize such tubes for tion for short periods may quickly develop so commercial use at frequencies; and with power much heart as to cause structural failure, by outputs, and under operating conditions herecollapse or puncturing of the glass envelope, or

tofore believed impossible of attainment. destruction of one or more of the interior ele- 35 It is an object of this invention to provide a ments, or otherwise. vacuum tube which will deliver substantially I have discovered that certain beliefs heretohigher output power at higher frequencies than fore considered as fundamental in tube design, the tubes heretofore known, without requiring are incorrect, and that certain factors heretothe use of forced cooling, such as by circulatfore regarded as immaterial, are of great im- 40 ing water. portance in the design and construction of high It is a further object of this invention to profrequency power tubes, and by applying my invide such a tube which is no more expensive to vention, I am able to produce tubes which may manufacture than the present types of tubes be identical with conventional prior art tubes as which are incapable of satisfactory operation regards the heretofore normally considered char- 45 under such conditions. acteristic determining essentials thereof, but It is a further object of this invention to which have greatly superior operating qualities, provide a tube capable of delivering relatively resulting from the embodying of features of my large power at ultra-high frequencies, and havinvention therein.

ing inter-electrode capacities of an order here- Comparing such prior art and improved tubes. 50 tofore believed too high to permit ultra-high they may have respectively filaments which are frequency operation. dimensionally and electrically identical, grids It is a further object of this invention to prosimilarly identical, and plates identical in length vide a tube of the class described which shall and material, differing only in their inside dihave a relatively long life when operating at ameter. Nevertheless, because of the incorpora- 55 tion of the features of my invention in such tubes, as will be more particularly described hereafter, they may be safely used under circuit conditions that would be practically instantaneously destructive to the prior art tubes, and at power outputs three to four times that of the prior art tubes. In addition, while the maximum frequency of such prior art tubes used at their full rating may be only 15 megacycles, the tubes of my invention may be used at their full maximum rating (which is much higher than that of the prior art tubes) up to frequencies as high as 60 mega'cycles.

Referring now more particularly to Fig. 1 in which I have illustrated a tube constructed in accordance with the principles of my invention, 1 designates the anode or plate, 2 the control electrode or grid, and 3 the cathode or filament.

In its preferred form the anode l is formed of a hollow shell of graphite or carbon machined to the desired dimension and shape and provided on opposite sides with integral longitudinal fins or flanges l by means of which the plate may be secured in position in the plate supports 3i and 38 as by means of rivets passing through the channeled plate supports and through the fin or flange l upon the plate.

The cathode, in this instance shows as a filament having a M convolution, is mounted at its lower end. upon leads 25 and 26 secured to heavy leads 22 and 23 which pass through the press 6 and are connected to base pins upon the base 5%.

As will be understood, the base of the stem 5 is joined to the envelope t at the bottom and the base 5!! is cemented thereto.

The upper bends of the filament may be held resiliently in position by means of wire hooks 3i and 32 terminating in coil springs 33 and 34- resting upon and passing through insulator 30,

which fits over and is secured to the upper end of rods i9 and it, around which the grid winding is wound and upon which it is carried. The

convolutions of the .grid winding preferably surround the filament.

The lower ends of rods 9 and M are secured, as by welding, to a metallic ring or collar 8 which, in turn, surrounds a tubular extension I arising from the press t. The upper end of the tubular extension l arising above the press is preferably left open and the upper edge of the collar 8 may be provided with a series of small fingers 8 bent inwardly over the edge of the glass tubing to prevent the collar slipping down out of position. The opposite ends H and E2 of the collar 8 may be bent outwardly to form projecting ears provided with openings l3 and i l for receiving bolt i5 passing through the openings and which bolt engages a nut m by means of which the collar may be clamped in position about the tubing. A shouldered insulating bushing l! is preferably inserted between the head of the bolt and the collar 3 to insulate the two ends thereof from each other.

This insulation serves two purposes. First, it permits higher degassing oi the tube by induction heating of the anode, by interrupting the electrical continuity of the grid supporting collar In the de-gassing operation in the bombarding machine, a high frequency current is induced in the conducting elements of the tube by placing outside the envelope a coil carrying high frequency current. If the collar were not insulated at its end, it would form a closed circuit and care would have to be taken during the bombarding not to permit this collar to get too hot (by stopping or decreasing the heating at intervals). Such over-heating would result in cracking the glass or weakening it at the stem, permitting leakage and ultimate failure of the tube. My construction permits the anode and other metallic parts of the tube to be heated continuously by high frequency bombardment to higher temperatures, thus permitting better degassing with less danger to the tube, and co-acting with the other features herein described to provide a tube capable of operating at higher frequencies with higher power outputs. Secondly, the construction decreases the losses due to absorption and dissipation of energy which would otherwise occur in the collar when the tube is operated at ultra-high frequency, because of the fact that, being interrupted by insulation the collar cannot operate as a closed circuit conductor in the high frequency field.

The anode, or plate, as previously stated, may be secured to the channel supports 31' and 38, which extend upwardly and inwardly and may be secured as by welding to a metal collar, or ring, 36, similar in construction to the collar 8 already described, the ring 35 surrounding stem 35 attached to the upper portion of the envelope A. The ring 3% may be formed to provide ears 44 to be engaged by bolt 45 and a similar insulating bushing ll may be interposed to prevent electrical continuity in the ring 36. Getter cups i9 and i! may be secured respectively to channel supports El and 38 by means of wires 42 and 43,

the cups being open away from the grid and plate structure, as in Fig. l the cups being open at the top. Prior to exhaustion of the tube, the getter material which is to be flashed may be placed within said cups. On flashing of the getter it will be deposited as a thin layer, or film 46 upon the interior portion of the envelope and stem above the getters cups.

The plate cap 5i may be cemented to the upper portion of the envelope 1 and is preferably made relatively large in size, extending downwardly to cover substantially the entire neck portion of the envelope, or if no neck is present to cover substantially all of the portion of the envelope where the getter is deposited, and connection to the plate or anode is made by means of a lead-wire 5 I passing through the upper press at the lower extremity of stem 35 and connected to the supporting system for the plate. It will be seen that in operation the plate, the supports 37 and 38, the collar 36, the lead-wire passing to plate cap 54, and the plate cap itself are all at the same potential. It will also be noted that the grid-filament assembly, on the one hand, and the plate assembly, on the other, are not mechanically connected by any bracing structure,

and are vacuiun insulated from each other.

I have found that the positioning of the getter, as described, contributes substantially to the improved operating characteristics of the tube.

If the getter were deposited in its usual position on the side or bottom of the bulb, the getter deposit would act as a conductive plane which would increase the inter-electrode capacity of the tube by its mutual relation to the grid, plate and. filament elements of the tube. In addition, there would also be established relatively intense electrical fields around the edges of the getter deposit adjacent the internal electrode of the tube, which would cause local heating by dielectric absorption of energy in the glass of the envelope. Thi local heating reduces the efiiciency of th tube and may cause bulb failure evidenced by local deflection or puncturing of the envelope in operation. These electrical fields may occur externally as well as internally of the tube.

Depositing the getter as explained with reference to Fig. 1, places the getter deposit 46 entirely or very substantially within the anode or plate cap, so that it is shielded by the said cap from outside electrical influences, and also places it in a relatively weak electric field because the cap and the more massive internal elements, such as the plate supporting collar, the plate supporting channels and the plate itself, are all at the same electrical potential at all times and consequently little or no dielectric field exists in the envelope at the edges of the getter deposit to produce local heating.

When the getter is in this position, the interelectrode capacity of the tube is a minimum low, because the getter deposit has a minimum mutual capacity to the anode, cathode and control electrode. If each of these elements have substantial capacity to a getter deposit, the interelectrode capacity of the elements themselves will be thereby increased.

Preferably, connection to the grid or control electrode is made through a side terminal or grid cap 20 through lead 18 passing through the envelope and connected at its outer end to the grid cap and at its inner end through flexible leads 19 to one of the grid supporting rods I0. The conductor I!) may and preferably will be made up of a number of fiat metallic ribbons secured together at their ends. Preferably the grid cap 20 is mounted upon a stand-off insulator 2i positioned under the grid cap and between it and the envelope 4 and cemented to the envelope 4. This serves to prevent corona discharge from the edge of the grid cap along the envelope in the direction of the plate, because of the intense electrical field between the grid and the plate, which would cause local heating of the bulb at the upper edge of the grid cap and thus result in possible bulb failure by sucking in or puncturing.

In the design of a power tube for operation at high frequency, the separation between the grid and the filament on the one hand and the plate and the grid on the other is particularly important. In this connection it is important to note that, despite earlier beliefs to the contrary, the plate resistance and mutual conductance per unit area does not depend upon the spacing of the grid to filament and plate to filamerit, but solely upon the grid to filament spacmg. I

The important feature in the design of such a tube is to relate the separation between the grid and filament, on the one hand, and the plate and grid on the other, so that the ratio of grid to plate transconductance, or mutual conductance, to the inter-electrode capacity and particularly, to the most important grid to plate capacity, is a maximum.

In this connection, by way of example, it may be stated that in two tubes in which the grid and filament spacings are the same, but the plate to grid spacing three times as large in the one as in the other, and in which the construction is otherwise the same in both tubes, at the same space current, the mutual conductance of a tube according to my invention and having the larger plate-grid spacing, is actually higher than that of the other tube with the lower plate-grid spacing.

Any changes in the internal construction and arrangement of the tube which cause this ratio to depart from its maximum value will result in reduced efficiency and reduced frequency at which the tube may be employed at its full ratmg.

While I have shown and described certain preferred embodiments of my invention, it will be understood that modification and changes may be made without departing from the spirit and scope of my invention as will be clear to those skilled in the art.

I claim:

1. A power tube capable of operation at ultrahigh frequencies, comprising an evacuated envelope, cathode, anode, and control electrodes positioned within said envelope, a conducting anode cap positioned on the outside of said envelope, and a conducting getter deposit on the interior of said envelope, said anode cap covering substantially all of the portion of the envelope Where the getter is deposited.

2. A power tube capable of operation at ultrahigh frequencies, comprising an evacuated envelope, cathode, anode, and control electrodes positioned within said envelope, a conducting tubular anode cap positioned on the outside of said envelope, and a conducting getter deposit within said envelope and substantially entirelywithin said anode cap.

3. A power tube capable of operation at ultra high frequencies, comprising an evacuated envelope, cathode, anode, and control electrodes positioned within said envelope, a conducting anode cap positioned on the outside of said envelope, and a conducting getter deposit on the interior of said envelope, said anode cap covering substantially all of the portion of the envelope where the getter is deposited, and the ratio of control electrode-anode transconductance to control electrode-plate capacity being a maximum.

4. A power tube capable of operation at ultra high frequencies, comprising an evacuated envelope, cathode, anode, and control electrodes positioned within said envelope, a conducting tubular anode cap positioned on the outside of said envelope and a conducting getter deposit within said envelope and substantially entirely within said anode cap and the ratio of control electrode-anode transconductance to control electrode-plate capacity being a maximum.

ALEXANDER SENAUKE. 

